My friend has a PC which started off as just XP. After a few years, it started locking up repeatedly - seemingly at random.

I reinstalled Windows & made it dual-boot with VL6 (LILO to the MBR), with VL there as a backup in case Windows ever got in a mess.

It worked fine for several months then started locking up again. So, I told her to start selecting VL instead (at the LILO boot menu). To my surprise, the lockups continued as before.

More and more, they seemed to occur at boot time, so I thought it must be a corrupt MBR. I rewrote the MBR several times, but that didn't fix it.

Finally, it got so bad that, a lot of the time, a reboot didn't even bring up a LILO menu. So, I put a VL6 Light Live DVD in the DVD drive and got her to use that.

It STILL intermittently locks up !

So- its nothing to do with the MBR (VL Light doesn't need the MBR)- its not the hard disk (I ran a test on this and its 100% clean )- its not faulty DRAM (I ran extensive tests and no probs found at all)

As Bigpaws said, it could be heat related - loose or clogged heatsink or worn out fans. I have also seen these symptoms on old hardware that is starting to fail, be it be the motherboard, video card or other components. Not all computers last for decades.

Could be the power supply. If another one is available, you could test by switching the power supplies and see if the problem goes away. If another isn't available, it might be worth it to get a cheap one for testing purposes. --GrannyGeek

I did run extensive memory tests, so I think I can rule memory problems out.

I cleaned out the chassis of dust etc a while back and put some machine oil on the main fan axis so it now runs noiselessly.

I ran some cpu temperature tests a few days ago and nothing showed up as a problem.

I will look into a BIOS upgrade but I thought BIOS was only involved at bootup time. Some of the lockups have occurred at boot up but a lot of them are long after boot, so doesnt that rule out BIOS as a cause ?

Maybe I can find a utility to check the p/s as I dont have a spare. When the lockup occurs, the power is still on (or at least, the chassis LED's are on that indicate system power up).

I have got a spare video card - I could install that..

There was a power surge a year or so ago that burnt out the on-board LAN port. I had to install a separate LAN card to get going again. But if that had had a knock-on affect on the motherboard, surely the problem would be persistent not creeping/intermittent ?

fiddled about a bit more today, and then I noticed a smell and realised the fan on the power supply wasn't spinning . Looks like a p/s swap may do it - so the prize goes to Grannygeek

i know this is a bit off. but its also a good idea to clean out the tower about once a month. (ie getting all the dirt/dust/ect out of it) dirt/dust are fan killers. alot of people never think to clean the tower out. they just put it down hook it up and only worry about it when soemthing goes wrong.